1. Field of the Invention
The present invention relates to a light emitting apparatus and a method for manufacturing the light emitting apparatus, and particularly to a light emitting apparatus using a phosphor excited by light emitted from a light source as well as a method for manufacturing the light emitting apparatus.
2. Description of the Background Art
As a next generation light emitting apparatus that is expected to consume less electrical power, have compact size, and exhibit high brightness, a light emitting apparatus using a light emitting diode (hereinafter LED) is being looked to. Examples of the light emitting apparatus using an LED include an LED backlight for a liquid crystal display and an LED light bulb. A light emission unit of the LED backlight or LED light bulb emits light which is different from the original light emitted from the LED itself. Specifically, the light emission unit of the light emitting apparatus using the LED emits a mixture of light into which a part of the light from the LED is wavelength-converted by a phosphor, and the original light from the LED without being wavelength-converted by the phosphor.
Use of a nanocrystal as the above-described phosphor is expected to improve the luminous efficiency as compared with conventional phosphors. A nanocrystalline phosphor can freely control the color to be emitted, from blue (short wavelength) to red (long wavelength), by changing the particle size to exhibit the quantum size effect. Conditions under which the nanocrystal is fabricated may be optimized to eliminate variations in particle size distribution of the nanocrystal and thereby obtain a nanocrystalline phosphor with a substantially uniform particle size. The uniform particle size of the nanocrystal enables a narrow emission spectrum to be obtained.
An example of the light emitting apparatus using such a nanocrystalline phosphor is disclosed in Japanese Patent Laying-Open No. 2004-071357 (Patent Document 1). FIG. 14 is a schematic side view of a light emitting apparatus of Patent Document 1. The light emitting apparatus of Patent Document 1 uses, for a wavelength conversion unit, a phosphor made up of nanocrystal particles of different sizes. Phosphor particles are distributed so that particles of greater sizes are located closer to the light source. More specifically, a red phosphor, a green phosphor, and a blue phosphor are distributed in this order so that the red phosphor is closest to the light source. Here, the red phosphor is an InN based nanocrystal of the largest particle size emitting red light. The green phosphor is an InN based nanocrystal of an intermediate particle size emitting green light. The blue phosphor is an InN based nanocrystal of the smallest particle size emitting blue light.
FIG. 15 is a schematic diagram of a light emitting apparatus in Japanese Patent Laying-Open No. 2007-049114 (Patent Document 2). Light emitting apparatus 90 of Patent Document 2 includes a light emitting device 91 emitting primary light, and a wavelength conversion unit 92 absorbing a part of the primary light and emitting secondary light having a wavelength equal to or longer than the wavelength of the primary light. Wavelength conversion unit 92 includes multiple different phosphors 93, 94, 95 having respective emission wavelengths different from each other. At least one of these multiple different phosphors has an absorption band which is capable of absorbing the secondary light emitted from at least another one of the phosphors. Such a structure enables a light emitting apparatus of a high brightness with easy setting of the emission color to be implemented.